In the publication, “Small Antennas Based on CRLH Structures”, IEEE Antennas and Propagation Magazine, Vol. 53, No. 2, April 2011, an antenna device having a wide bandwidth design is disclosed, wherein the design includes application of a composite right-left-hand “CRLH-based” RF design to print penta-band handset antennas directly on the printed circuit board (PCS), and balanced-antennas for Wi-Fi access points.
An antenna device 101 based on the CRLH structure is shown in FIGS. 3A and 3B, for example, while FIG. 4 shows a relationship between return loss and frequency in the antenna device shown in FIGS. 3A and 3B.
The antenna device 101 includes grounding patterns 103 on front and back sides of a board 102. A top patch 104 is provided on the front side of the board 102, and this top patch 104 is connected to the grounding pattern 103 on the back side via a receiving passageway 106 and a line 105. Further, a feeding point 107 insulated from the grounding pattern 103 is provided on the front side of the board 102, and a conductive pad 108 extends from this feeding point 107. The conductive pad 108 extends from the feeding point 107 and is capacitive coupled with the top patch 104 leaving a predetermined gap therefrom. The shape of the top patch 104, the gap distance between the conductive pad 108 and the top patch 104 in capacitive coupling, and the length of the line 105 determine a resonant frequency and a bandwidth on a low frequency side (a side denoted by a reference sign A in FIG. 4) of a first-order mode.
On the other hand, on the front side of the board 102, a meander line 109 extends from the middle of the conductive pad 108 in a direction opposite to the top patch 104. The meander line 109 is formed by folding back an elongated conductive pad many times. The shape of the meander line 109 determines a resonant frequency and a bandwidth on a high frequency side of a first-order mode (the side denoted by a reference sign B in FIG. 4) and those of third-order to fifth-order modes (the third-order mode is denoted by a reference sign C in FIG. 4).
By capacitive-coupling the resonance on the low frequency side of the first-order mode and resonance on the high frequency side of the first-order mode, a wider bandwidth can be obtained than in the case of using only resonance on the low frequency side.
However, the antenna device 101 shown in FIGS. 3A and 3B has the following problems, among others.
That is, adjustment of the resonant frequency on the high frequency side of the first-order mode is performed by changing the length, width, and pitch of the meander line 109, but such a problem is involved that the adjustment is complicated and difficult. Similarly, adjustment of the resonant frequency on the low frequency side of the first-order mode is performed by changing the lengths and shape of the top patch 104 and the line 105, but the adjustment is also complicated and difficult.
Further, adjustment of the bandwidth on the high frequency side of the first-order mode is performed by changing the width and pitch of the meander line 109, but the adjustment is also complicated and difficult.
Similarly, adjustment of the bandwidth on the low frequency side of the first-order mode is performed by changing the shape of the top patch 104 and the line width of the line 105, but the adjustment is also complicated and difficult.
In addition, adjustment of the capacitive coupling of the first-order mode is performed by changing the interval between the conductive pad 108 and the top patch 104, but the adjustment is also complicated and difficult.